In hermetic compressor units, oil is drawn from a sump by a lubrication pump to provide lubrication to the compressor. The compressor operation takes place over a range of conditions including transient conditions such as suction pressure drop at start up, shell pressure equalization, flooded start up, ambient swings and unit control changes. These transient conditions are often out of the range of normal steady-state operating conditions and can have serious consequences even though the transient conditions do not themselves persist. For example, the oil normally contains entrained refrigerant so that, if there is a sudden pressure drop at the suction inlet of the oil pump, a great deal of foaming and outgassing of the entrained refrigerant can take place. As a result, foam can be delivered to the lubrication system and the gaseous refrigerant can persist in the lubrication system thereby causing improper and/or inadequate lubrication.